emacs/lisp/textmodes/html-ts-mode.el

;;; html-ts-mode.el --- tree-sitter support for HTML  -*- lexical-binding: t; -*-

;; Copyright (C) 2023-2025 Free Software Foundation, Inc.

;; Author     : Theodor Thornhill <theo@thornhill.no>
;; Maintainer : Theodor Thornhill <theo@thornhill.no>
;; Created    : January 2023
;; Keywords   : html languages tree-sitter

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Tree-sitter language versions
;;
;; html-ts-mode is known to work with the following languages and version:
;; - tree-sitter-html: v0.23.2-1-gd9219ad
;;
;; We try our best to make builtin modes work with latest grammar
;; versions, so a more recent grammar version has a good chance to work.
;; Send us a bug report if it doesn't.

;;; Commentary:
;;

;;; Code:

(require 'treesit)
(require 'sgml-mode)

(declare-function treesit-parser-create "treesit.c")
(declare-function treesit-node-type "treesit.c")

(defcustom html-ts-mode-indent-offset 2
  "Number of spaces for each indentation step in `html-ts-mode'."
  :version "29.1"
  :type 'integer
  :safe 'integerp
  :group 'html)

(defvar html-ts-mode--indent-rules
  `((html
     ((parent-is "fragment") column-0 0)
     ((node-is "/>") parent-bol 0)
     ((node-is ">") parent-bol 0)
     ((node-is "end_tag") parent-bol 0)
     ((parent-is "comment") prev-adaptive-prefix 0)
     ((parent-is "element") parent-bol html-ts-mode-indent-offset)
     ((parent-is "script_element") parent-bol html-ts-mode-indent-offset)
     ((parent-is "style_element") parent-bol html-ts-mode-indent-offset)
     ((parent-is "start_tag") parent-bol html-ts-mode-indent-offset)
     ((parent-is "self_closing_tag") parent-bol html-ts-mode-indent-offset)))
  "Tree-sitter indent rules.")

(defvar html-ts-mode--font-lock-settings
  (treesit-font-lock-rules
   :language 'html
   :override t
   :feature 'comment
   `((comment) @font-lock-comment-face)
   :language 'html
   :override t
   :feature 'keyword
   `("doctype" @font-lock-keyword-face)
   :language 'html
   :override t
   :feature 'definition
   `((tag_name) @font-lock-function-name-face)
   :language 'html
   :override t
   :feature 'string
   `((quoted_attribute_value) @font-lock-string-face)
   :language 'html
   :override t
   :feature 'property
   `((attribute_name) @font-lock-variable-name-face))
  "Tree-sitter font-lock settings for `html-ts-mode'.")

(defun html-ts-mode--defun-name (node)
  "Return the defun name of NODE.
Return nil if there is no name or if NODE is not a defun node."
  (when (string-match-p "element" (treesit-node-type node))
    (treesit-node-text
     (treesit-search-subtree node "\\`tag_name\\'" nil nil 2)
     t)))

(defun html-ts-mode--outline-predicate (node)
  "Limit outlines to a few most meaningful elements."
  (let ((name (html-ts-mode--defun-name node)))
    (and name (string-match-p
               (rx bos (or "html" "head" "script" "style"
                           "body" (and "h" (any "1-6"))
                           "ol" "ul" "table")
                   eos)
               name))))

;;;###autoload
(define-derived-mode html-ts-mode html-mode "HTML"
  "Major mode for editing Html, powered by tree-sitter."
  :group 'html

  (unless (treesit-ready-p 'html)
    (error "Tree-sitter for HTML isn't available"))

  (setq treesit-primary-parser (treesit-parser-create 'html))

  ;; Indent.
  (setq-local treesit-simple-indent-rules html-ts-mode--indent-rules)

  ;; Navigation.
  (setq-local treesit-defun-type-regexp "element")
  (setq-local treesit-defun-name-function #'html-ts-mode--defun-name)

  (setq-local treesit-thing-settings
              `((html
                 (sexp ,(regexp-opt '("element"
                                      "text"
                                      "attribute"
                                      "value")))
                 (list ,(rx (or
                             ;; Also match script_element and style_element
                             "element"
                             ;; HTML comments have the element syntax
                             "comment")))
                 (sentence ,(rx (and bos (or "tag_name" "attribute") eos)))
                 (text ,(regexp-opt '("comment" "text"))))))

  ;; Font-lock.
  (setq-local treesit-font-lock-settings html-ts-mode--font-lock-settings)
  (setq-local treesit-font-lock-feature-list
              '((comment keyword definition)
                (property string)
                () ()))

  ;; Imenu.
  (setq-local treesit-simple-imenu-settings
              '((nil "element" nil nil)))

  ;; Outline minor mode.
  (setq-local treesit-outline-predicate #'html-ts-mode--outline-predicate)
  ;; `html-ts-mode' inherits from `html-mode' that sets
  ;; regexp-based outline variables.  So need to restore
  ;; the default values of outline variables to be able
  ;; to use `treesit-outline-predicate' above.
  (kill-local-variable 'outline-regexp)
  (kill-local-variable 'outline-heading-end-regexp)
  (kill-local-variable 'outline-level)

  (treesit-major-mode-setup))

(derived-mode-add-parents 'html-ts-mode '(html-mode))

(if (treesit-ready-p 'html)
    (add-to-list 'auto-mode-alist '("\\.html\\'" . html-ts-mode)))

(provide 'html-ts-mode)

;;; html-ts-mode.el ends here